In conventional systems, a transmission adapts the output of an engine, such as an internal combustion engine, to a drive shaft of the vehicle. Transmissions are also used on fixed machines or in applications where rotational speed and torque are adapted to provide power to a drive shaft. Transmission systems can be particularly complex when two motors are used to power one drive shaft. Conventional systems typically require complex gear and clutch systems and it can be difficult to provide adequate lubrication and control of moving parts.